Characterization of new Salmonella serovars by whole-genome sequencing and traditional typing techniques

Serotyping forms the basis of all national and international surveillance networks for Salmonella. Public health microbiology is currently being transformed by high-throughput DNA sequencing,which opens the door to serovar determination using this powerful technique. Twenty-nine Salmonella isolates referred to the Public Health England between 1994 and 2004 for serovar identification were selected for this study,and they all presented with novel antigenic formulae. Results from a combination of traditional phenotypic and molecular assays were compared. Twenty-two isolates (76 %) were subsequently independently confirmed as new types; of these,18 (82 %) were grouped as Salmonellaenterica subspecies I,and four (18 %) were S. enterica subspecies II. In general,it is shown that there is concordance between the DNA sequence type and traditional phenotypic serotype,but it would be necessary to analyse a larger data set to confirm this. Traditional multilocus sequence typing (MLST) by Sanger sequencing also correlates to in silico whole-genome sequencing MLST. This permits the continuation of traditional serovar nomenclature alongside sequence type methods and enhances the ability to infer true phylogenetic relationships between isolates.